1. Field of the Invention
The present invention relates generally to a door construction for a vehicle, in particular to a door construction designed for a railway carriage.
2. Discussion of the Prior Art
A prior door construction of this kind comprises a one-leaved or two-leaved door, which through the intermediary of one or more brackets, secured to a rotatable, vertical shaft, can be opened or closed by rotating the shaft, and a drive means for rotating the rotatable shaft, which drive means acts through the intermediary of a linkage on a first arm secured to the rotatable shaft, and by means of which the door can be locked in its closed position.
Such a door construction is described in Dutch patent specification no. 122,533 in which the movement for opening and closing of the door or doors is obtained by means of a pneumatic cylinder. The linkage comprises an intermediate rod pivoted at one end to the arm, and at the other to a guide rod having a fixed pivot at its other end. The object of this linkage is to lock the door in its closed position, for which purpose, among other things, the intermediate rod is made shorter than the guide rod and the relative positions thereof are such that, in the closed position, the intermediate rod and the guide rod overlap each other, and thereby occupy a dead-center position relative to each other for locking purposes.
The prior door construction is also applicable to a two-leaved door. In the case of a two-leaved door, the intermediate rods are pivoted together at their ends by means of a single, rigid connecting rod, with the fixed pivots of the guide rods being arranged on opposite sides of the connecting rod, and the pneumatic cylinder acting on said connecting rod.
In the prior door construction, the number of pivots is considerable, namely ten in the case of a two-leaved door. In addition, the prior door construction does not offer the possibility, for example, in the case of failure of the central pneumatic system which operates the pneumatic cylinder, of manually opening the doors both from the inside and from the outside, at least not in a structurally simple manner.